In a display device in which image display is driven by current, whether current outputted from a drain of a Thin Film Transistor (TFT) in the drive circuit is stable or not may have a direct impact on the display effect of the display device.
Stable output current may be obtained by utilizing the current characteristics of a TFT in the saturation region. In this case, the current outputted by the TFT is related to the gate-source voltage and the width-to-length ratio of channel of the TFT, regardless of the magnitude of the source-drain voltage (the output resistance of the TFT is infinite). However, when the drain voltage of the TFT reaches up to a certain extent, a pinch-off region occurs in the channel, i.e., the length of the channel may be reduced, and the width-to-length ratio of channel may be varied. In this case, the change in the width-to-length ratio of the channel may cause a larger fluctuation in the current outputted by the TFT, thereby affecting the display effect of the display device.
Furthermore, the TFT in the related art has a larger dimension, which may lead to a smaller pixel aperture ratio when the TFT is applied in the display device. According to an industry standard, the luminance of a display should reach a certain level. A smaller aperture ratio implies that an aperture region per unit area should emit light with much higher luminance to compensate for the smaller aperture ratio. However, increasing the luminance of the aperture region per unit area would greatly decrease the lifetime of a luminescent material.